1. Field of the Invention
The present invention relates to a variable wavelength light source capable of locking a variable resonance wavelength.
2. Description of the Related Art
Various variable wavelength light sources that output variable-wavelength laser lights have been known. Specifically, there is provided a variable wavelength light source configured to output a laser light with a desired resonance wavelength by using only a single gain element and elements arranged outside the gain element to provide a function of locking a variable wavelength (see Patent Document 1 (WO/2005/041372), Patent Document 2 (US Patent 2002/0172239)). The Patent Document 1 discloses a technology for locking a wavelength at a desired resonance wavelength by selecting a wavelength using a variable wavelength mirror and performing a phase adjustment by controlling an electric current applied to the gain element. The Patent Document 2 discloses a technology for locking a wavelength at a desired resonance wavelength without using a wavelength selective element such as an etalon in a resonator. Patent Document 3 (Japanese Patent Application Laid-open No. 2004-191729) discloses a technology for suppressing a liquid-crystal driving voltage to below 10 volts by arranging a transparent electrode in an etalon cavity of a tunable liquid-crystal etalon filter.
However, the variable wavelength light sources described above are configured to perform both a power control of the gain element and a phase adjustment of the resonance wavelength by a current control. Therefore, the power control and the phase adjustment cannot be performed separately, resulting in making it difficult to perform wavelength-lock control in a precise manner. It is necessary to enhance the wavelength accuracy of a target wavelength by a wavelength selective element such as an etalon for selecting an exact wavelength in the variable wavelength light source.